This invention relates to composite structures made from layers of material that will not normally bond readily to each other. More particularly, it relates to a method and resulting structure whereby a polymeric plastic surface layer, formed from a setting resin, will bond more readily to a hydraulic cement-based layer of mortar, concrete or the like.
It is, on occasion, desirable to bond to a concrete surface a polymeric plastic finish. An example is the concrete burial vault with plastic liner described in Canadian patent application 2,062,518 by Michael Davidian (laid-open Sept. 14, 1992). In that reference a thermo-setting epoxy resin adhesive with solvent and surfactant is applied to the outer surface of a preformed thermoplastic resin liner. Before the adhesive is fully cured, wet flowable concrete is applied to the adhesive layer. The result is to bond the concrete to the liner. Earlier United States patents addressing similar technology are U.S. Pat. No. 3,439,461 and U.S. Pat. No. 3,787,545.
In another U.S. Pat. No. 3,949,144 to Duff a reinforced concrete construction is formed from alternate, integrally bonded layers of epoxy concrete containing resin and fibre reinforced epoxy resin. The resulting laminate is a thin-walled construction of reduced cost, due to the use of concrete.
According to one variant of the Duff invention a gel coat is spread over a mold, followed by a layer of chopped glass fibres and epoxy resin. To this last layer while still wet is then applied the resin-containing, wet cement mixture. This is followed by alternate layers of reinforced resin and cement to build-up strength. Thus, in the Duff invention, a polymeric resin with glass fibres imbedded therein is bonded to a hydraulic cement layer that, as well, contains a bonding resin.
Thin structures based on the use of polymer-enriched concrete have also been employed using a fine wire matrix for reinforcing. Sold under the trade mark PERMA PLATE, by Ferro-Mesh of Canada Inc. the technology for fabrication of a three dimensional reinforcing mesh is described in Canadian patent No. 1,145,228. Applications of this technology have been directed to providing a finishing layer to concrete structures such as bridge decks and industrial flooring. The PERMA PLATE ((trademark)) finish has also been applied over wooden decking, such as on a pier. PERMA PLATE technology is ideally suited to forming thin-shelled structures having the dimensional stability associated with hydraulic cement and concrete. Problems may be encountered, however, in bonding such material to resin finishes that are organically-based. For example, a more or less complete curing of the concrete at the interface between the resin layer and the concrete layer may be required for maximum bond strength. In an actual production scenario, this delay could amount to a week or longer, and would be unacceptable, particularly if the parts being produced were fairly large and had to be moved for further processing or assembly.
This invention is directed to an improved means for bonding a hydraulic cement-based material to a polymeric plastic surface. It further has as an objective the production of thin walled structures having a high quality resin-based finish on at least one surface, and the dimensional stability of concrete.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.
According to one broad aspect of the invention, a thin walled structure is formed by:
(1) laying a resinous, polymeric coat over a mold, such coat being preferably supported by reinforcing fibres imbedded in resin;
(2) distributing a mechanical coupling means, preferably a preformed wire grid or optionally silica sand, chopped glass or mineral fibres, or a combination thereof over the surface of the resin while such resin is soft enough to bind to and retain such coupling means across its surface without absorbing such coupling means fully within the resin so that parts of the mechanical coupling means remain partially exposed;
(3) allowing the resin to set to form an interface surface; and
(4) applying a hydraulic cement based layer over the surface of the resin to bond with the exposed parts of the mechanical coupling means.
The coupling means is in all cases made of a solid material compatible with bonding to both the resinous coat and to a hydraulic cement mixture. By this method a composite is produced having alternate resin and cement layers with the coupling agent present, and providing bonding, at the interface of the two layers.
Preferably, the hydraulic cement based layer is polymer-modified so as to be polymer reinforced or bonded and after xe2x80x9cmay bexe2x80x9d insert further; and may be further reinforced by reinforcing planar wire mesh or a three dimensional matrix imbedded therein. Where a wire grid coupling means is employed, such coupling means may be attached to the reinforcing wire mesh or matrix to improve bonding of the cement layer to the resin coat.
As a further variant, the wire grid coupling means may be pre-formed to facilitate such attachment. Thus, a field of protruding wire stubs on a base may be bonded in place by the resin to provide means to locate the reinforcing wire mesh prior to the application of the hydraulic cement, and to further improve bonding between the resin and cement layers. Alternately or simultaneously, the wire grid coupling means may be in the form of a planar grid with raised or corrugated portions intended to protrude above the resin. Such raised or corrugated grid may be further anchored within the resinous coat by applying and imbedding fibre reinforcement above the portion of the coupling means imbedded in the resin.
As a further variant, part of the reinforcing planar wire mesh or matrix of the cement-based layer may be embedded in the layer of wet resin laid over the interface surface before the hydraulic cement based layer has been applied, thereby serving as the coupling means and providing a bond directly between the resinous layer and the hydraulic cement based layer.
Preferably, the resin coat has an outer gel-coat layer to provide an external, molded outer surface with a high-quality finish the mold surface, as well as inner, fibre reinforcement.
As a further variant, silica sand and/or chopped, silica-based or mineral-based fibres are partially imbedded in the resinous polymeric coat as the coupling means and provide bonding between the resin and cement layers.
Where silica sand or other particulate coupling means is used alone to bond the resin and cement layers the cement layer should allowed to cure thoroughly before the part is moved or disturbed as premature handling could destroy the bond. With wire grid as coupling means the part may be carefully moved much sooner. Maximum bonding effect is achieved when the wire grid and particulate matter coupling means are used together. Maximum panel strength is achieved when the cement layer is reinforced with a wire matrix or two layers of flat wire mesh.
By this method, a thin walled structure of substantial size, such as a projection screen or a hollow shelter, can be formed, the gel coat providing a smooth finish. Because of the use of the hydraulic cement to provide body and support, such thin-walled structures exhibit improved dimensional stability under variable temperature conditions.
The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow.